They are made by Hogue; they're for the centennial and bodyguard (to fit the bodyguard, there's an insert to fill up the space). I like them because they cover the entire backstrap of a centennial, add room for a pinky, and have the "Tamer" insert where the web of the hand sits like on an X-Frame Hogue grip. They extend exactly 0.41" below the bottom of the J-frame.
I sure like Glocks, but when I go out at night, there's a S&W 638 in my pocket. I keep an assortment of 1911s around the house for home defense, and there's a Glock 19 in my bug-out bag. I like them all.